This invention relates to recovering olefin from an olefin production process. In particular this invention relates to recovering light olefin, such as ethylene or propylene, from an olefin production process, converting the olefin to alcohol, and converting the alcohol to olefin.
Light olefins, particularly ethylene and propylene, are important raw materials for organic chemical production. The present world demand for ethylene for example is about 80 million tons per year, with a majority of this demand from the polyethylene industry. The preparation of ethylene derivatives, including polyethylene, typically requires a highly purified ethylene raw material. An ethylene concentration of 99.9 mole % is typically required for polyethylene production. Obtaining ethylene and propylene at high purity requires difficult separations following the olefin production process.
One of the most difficult separations that occurs during the olefin production process is the removal of non-olefin by-products from desirable olefin products. The removal of by-products is desired to achieve high purity olefin products. The removal of these by-products can be a difficult and expensive task. Extremely low temperature separations are generally required to remove these components from certain olefin product streams. For this reason, various methods of reducing the separation requirements have been explored. For example, van Dijk, U.S. Pat. No. 5,811,621, and Kuechler et al. U.S. Pat. No. 4,960,643 disclose processes where a less rigorous process of removing methane by-product is used with a resulting higher concentration of ethylene product. The methane containing by-product is then either used for fuel gas or used to make ethylene derivatives with less strict purity requirements.
Several known process also exist for the production of alcohols from a stream containing olefins. Imai, U.S. Pat. No. 4,482,767 discloses a method of producing lower alcohols from a stream comprising hydrogen, methane, ethane, ethylene, propane, and propylene. The hydration of ethane using several catalysts is further discussed in Frampton, et al. U.S. Pat. No. 4,234,748.
A need exists, therefore, for recovery of olefin, e.g., ethylene and propylene, during the manufacturing process in order to reduce loss of olefins which could be used in making olefin derivative products. In particular, it is highly desirable to recover olefins which could be lost during separation of olefin products obtained from the catalytic conversion of oxygenate components.
In order to recover olefins which could be lost during separation of olefin products, this invention provides for hydrating olefins in a stream to produce alcohols. The alcohol can then be used to make olefin products.
In one embodiment, the invention provides a method of recovering olefin in an oxygenate to olefin reaction process. The method comprises reacting a stream containing olefin with water in the presence of a hydrating catalyst to produce an alcohol containing stream. The alcohol containing stream is combined with an oxygenate feed stream to produce a combined feed stream, and the combined feed stream is contacted with an olefin forming catalyst to form an olefin product stream.
Preferably, the hydrating catalyst is a phosphoric acid catalyst. Preferably, the olefin forming catalyst is a silicoaluminophosphate molecular sieve catalyst. Preferably, the alcohol containing stream contains ethanol or propanol. Preferably, the oxygenate feed is methanol. Preferably, the reaction of a stream containing olefin with water in the presence of a hydrating catalyst is performed at a temperature of 180xc2x0 C. to 300xc2x0 C. and a pressure of 350 psig to 1000 psig.
In another embodiment, the invention provides a method of producing olefins from oxygenates. The method comprises mixing an oxygenate feed stream with an alcohol containing stream, with the alcohol containing stream being produced from olefin in the olefin production process. The mixed oxygenate and alcohol feed stream is converted in the presence of an olefin forming catalyst to form an olefin product stream.
In another embodiment, the invention provides a method of recovering ethylene in an ethylene production process. The method comprises reacting a stream containing ethylene with water in the presence of a hydrating catalyst to produce an ethanol containing stream. The ethanol from the ethanol containing stream is combined with an oxygenate feed stream to produce a combined feed stream, and the combined feed stream is contacted with an ethylene forming catalyst to form an ethylene product stream.